Biomechanics 2 Flashcards
Kinematics definition?
describing motion without regard to the force producing the motion
What is rotation about an axis?
Angular motion to produce linear motion
When rotating around a bar what do different body positions do?
Influence resistance to rotation
What’s generalised motion?
Most sporting movements
Inlvolves both translation and rotation
How is curvilinear translation achieved?
via angular motion about joint centres
Whats a minute?
1/60 of a degree
Standard unit for angular velocity?
Radians
Its the ratio of the length of a circular arc (s) to the radius of the arc(r)
θ = 𝒓/s
How to convert degrees into radians?
divide by 57.3
What’s angular distance?
length of angular path
What’s angular displacement?
Difference between initial and final positions
What’s angular speed?
Angular distance / time
What’s angular velocity?
w = (change in angular position) / (change in time)
Units are radians/s
What’s angular acceleration?
Change in angular velocity / change in time
Units are radians/s^2
What’s a relative angle?
Between 2 different segments
Knee, ankle
What’s an absolute angle?
Angle defined relative to a line in space
Describes orientation of segment in space
Thigh, foot
When given 3 points with coordinates how to calculate the angle behind the knee?
Cosine rule: a^2 = (b^2 +c^2) - (2bc cos angle)
But first have to determine the 3 lengths via Pythagoras theorem
Rearrange to find the angle
= cos angle = (b^2 + c^2 - a^2) / (2bc)
Or you can use right angled triangles find the angles next to the one you want then do 180 - the 2 angles you have found using SOH CAH TOA
Is the first central difference method different using angles?
No
The ones around the subject subtract the divide by time, same for velocity and acceleration
Why does heel lift reduce potential for achilles tendon strain?
There is reduced ankle angle and no change in knee angle
Results in reduced ankle dorsi flexion so less likely to strain
Assumptions you make when finding angles on lower part of body?
Skin markers represent joint movement on the: Hip Knee Ankle MTP Heel
Rigid body segments
two-dimensional rotations
What are the phases of ground contact in running?
Footstrike - heel just landed
Initial support - foot flat
Mid stance - heel begins to lift off
Toe - off
Dixon and Kerwin (1999) found that heel lift devices reduced ankle dorsi-flexion while having no significant influence on knee joint motion. What did they conclude regarding Achilles tendon strain?
That Achilles tendon strain was reduced when using heel lift devices
What’s a good method of breaking down a performance?
Identifying of kinematic variables at key points, for example in a golfers swing just look at the backswing
What’s the kinetic chain?
For example when looking at a tennis serve and the maximum velocity of the tennis ball its been found that to achieve this the timing of peak angular velocities of the contributing body segments occur in an order from proximal to distal = the kinetic chain
Each segment produces a force and also acts as a stabilising structure for the next segment
So each segment has a stabilising phase followed by an acceleration phase
if segment fails other segments are compensated reduce in performance and increased chance of injury
Relationship between linear and angular motion?
Required to optimise performance in sports involving rotation
VT = rw
VT = tangenital velocity
r = radius of rotation
w = angular velocity
hence the relationship can be increased via increasing the radius of rotation or angular velocity
2 types of athletic injury?
Acute - are associated with a traumatic event such as those from a hard tackle or from falling
Chronic (overuse) - from result from repetitive action such as long distance running or repaired throwing
What are intrinsic factors (within the body)?
Age Sex Previous injury Aerobic fitness Muscle strength Reaction time Anatomical alignment Postural stability
What are extrinsic factors (outside the body)?
Footwear
Surface
Competition level
What’s dorsi flexion of the ankle?
Put your toe up
What’s Plantar flexion?
Putting toe down
What’s abduction of the foot?
Toe moving away from body
What’s adduction of the foot?
Toe moving towards the body
What’s rear foot inversion?
Sole of foot points inwards and upwards
What’s rear foot eversion?
Sole of foot points outwards and upwards
Parts of the foot and ankle complex?
Talocrural (Ankle) Joint (joins distal ends of the Tibia and Fibula with the proximal talus
Allows sagittal plane motion (plantar/dorsiflexion)
(should be drawn in the exam)
Subtalar joint:
Allows frontal and transverse motion
Possible advantages of allowing Pronation (eversion)?
Natural cushioning
Can adapt to surfaces
Allows tibial rotation
Rearfoot movement typical values?
4 degrees = 3.3 m.s^-1 (Willems et al 2005)
11 degrees = 3.7 m.s^-1 (Pohl et al 2009)
Limitations of injury research?
Many are cross sectional and retrospective
Large sample sizes are required
Injuries grouped together as overuse or running related
characteristics highlighted in shoe advertising?
Shock absorption / cushioning
Motion control / stability
Traction
Weight / energy
Comfort / fit
In rear foot motion the steps of supination and pronation?
Supination:
Inversion
Adduction
Plater-Flexion
Pronation:
Eversion
Abduction
Doris-Flexion
What is shoe stability?
The ability of the shoe to resist excessive or unwanted motion of the ankle
Quantified by rear foot motion
Shoe design features?
Shoe shape - heel flare
Shoe supportive features-
Medial posting - built up bit of the shoe on the medial side (stops you rolling inwards) - decreases rear foot motion
Dual density - doesn’t deform on a certain area
Orthotic devices - inserts in the shoe - reduce rear foot motion
What does increased medial heel flare do?
Reduced rear foot movement
